Micro-X Mission

Micro-X is a proposed sounding rocket payload that combines an X-ray microcalorimeter array with an imaging mirror to obtain breakthrough science from high spectral resolution observations of extended and point X-ray sources. Three possible targets of Micro-X include the Puppis A supernova remnant, the Virgo Cluster, and the Circinus X-1. For example, a Micro-X observation of the bright eastern knot of Puppis A will obtain a line-dominated spectrum with 90,000 counts collected in 300 seconds at 2 eV resolution across the .3-2.5 keV band. Micro-X will utilize plasma diagnostics to determine the thermodynamic and ionization state of the plasma, to search for line shifts and broadening associated with dynamical processes, and seek evidence of ejecta enhancement. For clusters of galaxies, Micro-X can uniquely study turbulence and the temperature distribution function. For binaries, Micro-X's high resolution spectra will separate the different processes contributing to the Fe K lines at 6 keV and give a clear view of the geometry of the gas flows and circumstellar gas.
The promise of imaging, high resolution X-ray spectroscopy is thus far unfulfilled. Micro-X is proposed to fill this gap, offering a unique combination of bandpass, collecting area, and spectral and angular resolution. The spectral resolution across the 0.3-2.0 keV band will be 2 eV. The angular resolution across the 14.4 arc minute field of view will be 2.5 arc minutes. The effective area, 200 square centimeters at 1 keV, is sufficient to provide observations of unprecedented quality of numerous cosmic X-ray sources, discrete and extended, even in a brief sounding rocket exposure.
The scientific program will initially focus on extended sources, for which high-spectral-resolution, wide-energy-bandwidth observations were hitherto impossible. For our initial flight, we will observe the bright eastern knot in the Puppis A remnant, a site of complex cloud-shock interactions and ejecta enrichment. Other SNRs for which breakthrough observations are possible include the Cygnus Loop and Cas A. The center of the Virgo Cluster is the highest priority cluster target. Eventually the payload can be reconfigured with the ASCA flight spare mirror to measure the velocity of accreting and outflowing gas in X-ray binary systems.
The scientific potential of the X-ray microcalorimeter for revealing high-precision spectral diagnostics is still largely unfulfilled, and the Micro-X payload will go a long way toward providing valuable experience and solutions to the practical problems of deploying TES microcalorimeters in space. By confronting the real issues of producing the payload and flying it, NASA will achieve a flight TES array, robust and compact electronics unique to these sensors, and obtain astrophysically rich data with a TES microcalorimeter. The science return from this mission will be substantial. Micro-X will obtain the first imaging X-ray microcalorimeter spectra from astrophysical objects, give the community a sampling of what future orbiting missions will accomplish, and serve as a pathfinder for other, future telescope missions.

how it works

The refrigerator works by cooling in stages. The first stage is of cooling is achieved by pumping liquid helium so that it absorbs heat from the surrounding area. Evaporated Helium from this area is released through the satellite to create temperature zones, with the center of the satellite and the detector array being the coldest of all. Pumping the liquid Helium can cool this area to 2-4 degrees Kelvin.

To cool the detector array from 2-4 degrees Kelvin down to 50 mK the satellite using an Adiabatic Demagnetization Refrigerator. This works by aligning dipoles in order to absorb heat. There is a salt pill which contains iron atoms bonded to large salt molecules at the center of the ADR. By turning on a powerful (4-5 tesla in this case) magnet the outer D orbital electrons in each iron atom are aligned. Since this is a higher energy state for the salt pill, it absorbs energy in the form of heat from whatever it is attached to. However the dipoles want to be randomized and when the field is turned off they do randomize, giving off heat. By using a heat switch to make sure it takes heat from the detector array and releases it elsewhere, the detector array can be cooled to these truly extreme temperatures by cycling the ADR.

what we are doing

The detector array uses SQUIDs as part of its photon sensing apparatus. The SQUIDs, as well as the detector itself are extremely sensitive to magnetic field, like that generated by the ADR's 5 tesla magnet. We have been tasked therefore with designing the magnetic shielding to protect them from this extreme field. The detector sits directly below the magnet so a strong effective shield must be made. However, since the mission is going up in a sounding rocket, the shield must also be lightweight durable and small.

did you know?

8/4/06

We are busy wraping things up and exprementing with different configuarions of sheilding.

7/16/06

We finally have fully sorted out our singular matrix problems by using only functions that have smooth derivates.

7/19/06

We have sorted out our COMSOL problems with singular matrix errors by using a non-linear solver.

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